Bulk material containing solid particles usually has a varying particle size distribution and/or mass distribution.
In the handling of such bulk material, which may consist e.g. of gravel, sand, asphalt or gravel mixtures, asphalt-concrete, moist concrete, or the like, the bulk material usually is separated into fractions containing coarser and finer particles. When a container is being filled with that type of bulk material by supply from above, e.g. from a point, the bulk material will form slope sides in the container along which coarser and/or heavier particles will fall down and collect at the foot of the slope to a greater degree than finer and/or lighter particles will do. This separation process occurs if the bulk material has a dry consistency, such as gravel, but also in the case of moist bulk material, such as wet cement-concrete wherein coarser and/or heavier particles will drop to the bottom of the container to form slopes in a corresponding way. This will cause a separation inside the container into regions containing coarser and/or heavier particles and regions containing finer and/or lighter particles, but the sizes of these regions will depend on variations in composition of the supplied bulk material. During the feeding out of the bulk material from the container by means of continuously working conveyors, such as worm conveyors, endless conveyor belts, continuously working scraper conveyors, tube conveyors and the like, the size and/or mass distribution of the particles will vary in the fed out material. For example, at the feeding out of asphalt mixtures for road surfacing one has observed a separation of the particle shaped material into coarser and finer fraction, in the road surface, which has led to impaired wear resistance due to the fact that a certain size fraction may be missing while an other one may exist in excess although the material which was supplied had a proper particle size distribution.